Room: AAPM ePoster Library
Sophisticated radiation therapy techniques offer the ability to deliver large amount of radiation to target while sparing the surrounding organs at risk (OARs). However, these sophisticated techniques may not be always available to all patients, particularly to palliative patients. Typical palliative treatment for lesions located in the spine is opposing AP-PA beams. While lesions receive the prescription dose, so does the small bowel. This lead to acute small bowel toxicity. Soyfer etal. in 2013 addressed this issue and suggested the use of 3-fields (LAO, RAO, PA) as opposed to AP-PA beams. This study presents opposing conformal arcs as an alternative to reduce high dose to the OARs.
Three patients with lesions in the vertebrae treated in our institution during 2019 -2020 were randomly selected for this study. Besides the clinically treated AP-PA plan (30Gy in 15fx), additional 3-field plans and opposing conformal arc (2-arc) plans were generated. All plans were then normalized so that the vertebrae structure receives same prescription coverage (D95). Doses to small bowl, particularly the V30, V50, V70 and V90, were recorded and compared among the 3 plans.
On average, V70 and V90 of the small bowel in the 3-field plans (3.1%,0.04%) and opposing arc plans (0.2%,0.03%) are remarkably lower than the AP-PA plans (11.5%,9.8%). While V50 is comparable between the 3-field plan (14.1%) and AP-PA plan (12.8%), the opposing arc plan further reduced V50 to 3%. However, V30 of the 3-field plans (19.6%) and opposing arc plans (20.7%) were larger than the AP-PA plans as the trade-off for the decrease high dose volume.
Our study validated Soyfer etal. conclusion that the 3-field technique is clinically superior to the AP-PA technique. However, the opposing conformal arcs provides an option to further reduce high dose in the small bowel without appreciable additional effort.
Not Applicable / None Entered.